On the 9th of July 2020 geotechnical drilling began along the proposed route of the Mitchell Treaty Tunnels (MTT), a key infrastructure component of the KSM gold-copper project in north western British Columbia, Canada. The permit for the drill program was obtained from the BC government on the 30/06/20.
The Mitchell – Treaty Tunnels (MTT) are 22.7 km twin tunnels which will connect the Mitchell Mine Site with the Treaty OPC and TMF. One tunnel is for conveying ore, the other for transporting materials, personnel and power. The conveyor tunnel is designed as 6 m wide by 4.3 m high and will convey ore from the open pits in the Mitchell Valley to the Process Plant.
The transport tunnel is 4.5 m wide by 4.3 m high and has been located 30m to the north of the conveyor tunnel. This tunnel will be used to transport crews and materials. Cross-cuts will connect the tunnels every 300 m. The 30 m separation between the MTT is very important for development and operation of the MTT. 30 m is needed for geotechnical stability and the cross-cuts are needed for ventilation control, electrical sub-stations, emergency safety chambers, remuck bays, maintenance bays, ventilation control doors and water control infrastructure.
The MTT alignment runs roughly east-west, starting in the west from the Mine Site in the Mitchell valley at an elevation of 850 m asl, to a Saddle Area at km 16, where a portal will provide entry for construction works, and another 6 km section from the Saddle Area to the Treaty OPC at an elevation of 1080 masl. Five portals (two Mitchell Portals, one Saddle Portal and two Treaty Plant Site Portals) are proposed for construction of the MTT, from west to east starting with km 0.
Plans include a proposed construction access adit, however, due to potential geohazards, the Construction Access adit is to be considered as a contingency only if there are significant delays at other construction fronts. The contingency plan allows for construction of a 364 m long 15.5% slope construction access adit.
Geological settings along the MTT alignment are complex; the area has been subject to normal and thrust faults, and the route traverses contacts, unconformities, folding and areas of extensive alteration. The geologic and geotechnical conditions described are based on information inferred from limited surface mapping (40% of the MTT tunnel route is beneath icefields), and from widely spaced drill holes. Additional geotechnical investigations to be performed in detailed design stages will reduce geotechnical uncertainty and reduce the risk of unexpected delays in tunnelling.
This year's drilling will consist of about 4,000 m in 10 holes to obtain information on the condition of the rocks through which the tunnels will be driven. This data will help in the selection of the best excavation technology for tunnel construction. Instrumentation will also be installed for ongoing data collection that will further assist tunnel design. Later this summer Seabridge plans to undertake a geophysics and short borehole drill program to determine foundation properties for construction of one of the MTT''s key portals. For further information please visit http://www.seabridgegold.net and
https://ksmproject.com/project/mitchell-treaty-tunnel-permits/. 29/20.
